Getting frequency/spectrum from audio

User Code & Projects
1

Hi, i want to get the current freuency/spectrum from the AudioNode, how can i achieve that?
I found this one link, but i don’t get it what this guy is meaning at all.
My goal is something like that: [video]http://www.youtube.com/watch?v=nuHmMh3vXhU[/video]

kind regards
sytrox

2

Well if you don’t know what FFT is you will probably have a hard time doing that…

To not come across like an asshole by just saying that, heres some FFT code that might be helpful as soon as you know how :slight_smile:

[java]/*************************************************************************

  • Compilation: javac FFT.java
  • Execution: java FFT N
  • Dependencies: Complex.java
  • Compute the FFT and inverse FFT of a length N complex sequence.
  • Bare bones implementation that runs in O(N log N) time.
  • Limitations
    • assumes N is a power of 2
    • not the most memory efficient algorithm

*************************************************************************/

package kleinehummel;

/**
*

  • @author normenhansen
    */

public class FFT {

// compute the FFT of x[], assuming its length is a power of 2
public static Complex[] fft(Complex[] x) {
    int N = x.length;
    Complex[] y = new Complex[N];

    // base case
    if (N == 1) {
        y[0] = x[0];
        return y;
    }

    // radix 2 Cooley-Tukey FFT
    if (N % 2 != 0) throw new RuntimeException("N is not a power of 2");
    Complex[] even = new Complex[N/2];
    Complex[] odd  = new Complex[N/2];
    for (int k = 0; k < N/2; k++) even[k] = x[2*k];
    for (int k = 0; k < N/2; k++) odd[k]  = x[2*k + 1];

    Complex[] q = fft(even);
    Complex[] r = fft(odd);

    for (int k = 0; k < N/2; k++) {
        double kth = -2 * k * Math.PI / N;
        Complex wk = new Complex(Math.cos(kth), Math.sin(kth));
        y[k]       = q[k].plus(wk.times(r[k]));
        y[k + N/2] = q[k].minus(wk.times(r[k]));
    }
    return y;
}


// compute the inverse FFT of x[], assuming its length is a power of 2
public static Complex[] ifft(Complex[] x) {
    int N = x.length;

    // take conjugate
    for (int i = 0; i < N; i++)
        x[i] = x[i].conjugate();

    // compute forward FFT
    Complex[] y = fft(x);

    // take conjugate again
    for (int i = 0; i < N; i++)
        y[i] = y[i].conjugate();

    // divide by N
    for (int i = 0; i < N; i++)
        y[i] = y[i].times(1.0 / N);

    return y;

}

// compute the convolution of x and y
public static Complex[] convolve(Complex[] x, Complex[] y) {
    if (x.length != y.length) throw new RuntimeException("Dimensions don't agree");
    int N = x.length;

    // compute FFT of each sequence
    Complex[] a = fft(x);
    Complex[] b = fft(y);

    // point-wise multiply
    Complex[] c = new Complex[N];
    for (int i = 0; i < N; i++)
        c[i] = a[i].times(b[i]);

    // compute inverse FFT
    return ifft(c);
}



// test client
public static void main(String[] args) { 
    int N = 128;
    //double start=.getTimeInMillis();
    
    Complex[] x = new Complex[N];

    // original data
    for (int i = 0; i < N; i++) {
        x[i] = new Complex(i, 0);
    }
    for (int i = 0; i < N; i++)
        System.out.println(x[i]);
    System.out.println();

    // FFT of original data
    Complex[] y = fft(x);
    for (int i = 0; i < N; i++)
        System.out.println(y[i]);
    System.out.println();

    // take inverse FFT
    Complex[] z = ifft(y);
    for (int i = 0; i < N; i++)
        System.out.println(z[i]);
    System.out.println();

    // convolution of x with itself
    Complex[] c = convolve(x, x);
    for (int i = 0; i < N; i++)
        System.out.println(c[i]);

}

}
[/java]

2 Likes